How Many Wives Will I Have?

For every 12 mangos that I buy,3 turn out to be rotten.At this rate,how many rotten mangoes will I have if I buy 100 mangoes?

For every 21 apples that i buy,3 turns out to be rotten.How many rotten apples will I have if I buy 100 apples.

How many sides does an octagon have?

A and B each have a certain number of mangoes.A says to B, if you give 30 of your mangoes,I will have twice as many as left with you.B replies,if you give me 10, I will have thrice as many as left with you.How many mangoes does each have?